Babies change dramatically during their first three years of life, and perhaps no changes are more dramatic than those that happen in the brain. The cognitive development of children is at its most astounding during the first three years of life, when the brain grows to 90 percent of its adult size. A 19-month-old baby is considered a toddler, and brain development during this time is rapid.

Cognitive Development

According to the California Department of Education, cognitive development is the formation and development of skills related to thinking, reasoning and understanding. This includes language skills. Cognitive development is also the acquisition and compartmentalization of knowledge. As your baby grows, he learns more and more about the relationships between people and objects -- including his relationships in his world. By the time your child is 19 months old, he has learned he is a person apart from his mother.

Receptive Language Development

Receptive and expressive language development is an important part of brain development. In general, toddlers usually understand more than they can express. A 19-month-old can usually follow simple commands, such as "sit in your chair" even though she may not be able to tell you what she wants for dinner. Because she is always thinking about the relationships between things and how they work, she may start asking you "why" questions at this age. Go ahead and explain why -- she is taking it all in, even if she can't repeat exactly what you say.

Expressive Language Development

Toddlers vary widely in their expressive language skills -- some toddlers will only know approximately 10 words, while others will use five times as many words -- but, by the time toddlers are 19 months old, they are usually able to use a few verbs and put two words together. Direction words are also common at this age, and a 19-month-old may also be able to predict words in familiar stories, identify objects around the house and sing simple songs.

Emotional Development

Emotional development starts in the brain when a toddler begins to figure out how and why people interact with each other. This is one reason why the "terrible twos" usually start near 18 or 19 months of age. Your child has realized she can be separated from you and may voice displeasure at this new development. Children of this age are also starting to wonder what will happen if they act in certain ways, such as pulling your hair or poking a younger sibling in the eye. Although this is a trying time for parents, it's an important phase of cognitive development.

Problem-Solving

Problem-solving is another important part of cognitive development. A 19-month-old will start to try to solve problems -- including getting those childproof locks unlocked -- and may even work together with another child to get what he wants. These problem-solving abilities often manifest in classification and sorting activities, and you may even see them appear at dinner when your child suddenly only wants to eat yellow food.